The present invention relates generally to an exposure apparatus, and more particularly to an exposure apparatus used to manufacture various devices including semiconductor chips such as ICs and LSIs, a display device such as a liquid crystal panel, a sensing device such as a magnetic head, an image pick-up device such as a CCD, and a fine pattern for micromechanics. The present invention is suitable, for example, for a maskless exposure apparatus that utilizes a spatial modulation element, such as a micro-mirror array, and a projection type image display unit, such as a projector that displays an image on a screen.
Due to the demand by the large personal computer (“PC”) market, the fine processing of the semiconductor integrated circuits (“ICs”) has rapidly developed, and the design rule of 90 nm has been achieved. Many devices are produced as highly versatile and marketable microprocessor units (“MPUs”) and memories for use with the PCs. These MPUs and the memories use the same devices even for different PC manufacturers and models, and the same semiconductor devices are manufactured in huge quantities.
The information appliances are expected to be the largest market in the future for the semiconductor devices along with the widespread digital TVs, versatile cellular phones, networks, etc. The information appliances use unique semiconductor devices (or system LSIs) suitable for their manufacturers and models, and require the manufacture of various types of devices. The information appliances are designed and produced based on consumers' demands. Various consumers' demands require the manufacture of various products, and limit the number of units produced per model. Individual demands are so fluid that the products need to be put onto the market at the proper times based on the consumers' demands.
For the conventional semiconductor devices typified by the MPUs and memories, the same model can be produced in large quantities over a long time period of time. On the other hand, for the semiconductor devices (or system LSIs) in the information appliances, various types should be produced in small quantities only for a short time period and put onto the market at proper times.
A projection exposure apparatus, which has conventionally been used, projects a circuit pattern of a mask (or a reticle) onto a wafer etc. via a projection optical system and transfers the circuit pattern in a lithography that serves as the important technology for production of the semiconductor devices. For the fine processing and the high integration of the semiconductor devices, the projection exposure apparatus can now transfer a pattern smaller than the exposure wavelength by using, for example, a phase shift mask, etc. The phase shift mask is more complicated and thus more expensive than a conventional binary mask.
If the duplicate device is produced in large quantities, the mask cost per device is reduced. However, when the number of produced system LSIs are low, a mask cost increases, which makes the device and mask expensive, such as the phase shift mask. The information appliances are subject to keen price competitions similar to conventional home electric appliances, and preferably avoid use of expensive semiconductor devices.
Accordingly, use of a direct imaging type of exposure apparatus (or a maskless exposure apparatus) to produce the system LSIs attracts attention. The maskless exposure apparatus uses no mask, and can start producing the devices without producing a mask once a device circuit design is determined. The maskless exposure apparatus eliminates the mask cost, and reduces the device producing time period.
The maskless exposure apparatus includes a pattern generator that has plural pixels, such as a micro-mirror and a liquid crystal, on a substrate. The pattern generator is located at a position corresponding to a mask position in a conventional exposure apparatus, and generates a circuit pattern. See, for example, U.S. Pat. No. 5,330,878. More specifically, the pattern generator generates a circuit pattern by independently driving the pixels and by controlling their reflections and non-reflections of the light.
The pixels in the pattern generator are required to have the mechanical durability to drive. However, adhesion actually restrains the driving between adjacent mirrors and between the mirror and the substrate due to mixture of foreign matter with mirror's deformations.
Accordingly, there are various proposals including microwave irradiations onto the pixels in the pattern generator so as to prevent restraints of driving of each pixel, and continuous driving of each pixel. See, for example, U.S. Pat. Nos. 5,412,186 and 6,544,698.
While the prior art disclose an anti-adhesion approach for the mirror, the instant inventor has discovered that the pattern transfer precision deteriorates due to a change of the mirror's reflectance, etc. For example, while microwave irradiations prevent the mirror's adhesion as taught by U.S. Pat. No. 5,412,186, a defect occurs in a circuit pattern generated by the pattern generator when the reflectance changes as a result of the foreign matter or contaminants adhering to the mirror surface. In other words, the prior art does not consider a change of the optical performance of the mirror.
It is also discovered that the microwave irradiations and mirror's continuous driving do not always prevent the mirror's adhesion.
It is conceivable to exchange the micro-mirror array when the optical performance changes due to the mirror's adhesions. However, a maintenance person needs a long time to exchange and position the micro-mirror array because of the optical-axis alignment in the procedure, causing the lowered throughput of the devices, such as a semiconductor, due to the downtime.
The liquid crystal is subject to similar problems as the micro-mirror array. The liquid crystal has a problem of transmittance changing corresponding to the mirror's reflectance changes, although the liquid crystal does not suffer from a problem corresponding to the mirror's adhesion. A defect occurs in a circuit pattern similar to that in the micro-mirror array when the liquid crystal pixels lower the transmittance.